Introduction to Client-Side Javascript

Course Evaluation

 5 lectures and 5 labs

 Evaluation:
 60% Project and Assignments
 40% Labs and Quizzes

Lecture Outline

 Introduction

 JavaScript Syntax

 Built-in objects

 Functions

How did it all start?

 Invented by Brendan Eich at Netscape

 First appeared in Navigator 2.0 browser.

 Appeared since Microsoft Internet Explorer 3.0.

What JavaScript isn‟t?

 It isn‟t Java

 It isn‟t HTML or a version of it

 It isn‟t compiled

 For Client-Side JS:
 It has no graphics capabilities, except for the powerful
ability to dynamically generate HTML.
 It isn‟t allowed the reading or writing of files.
 It has no support for networking of any kind.

What JavaScript is?
 It is a scripting language, to be processed and executed
by a JavaScript interpreter.

 It is dynamic.

 It is Object Oriented or Object-based (controversial
subject).
 "ECMAScript is an object-oriented programming language
for performing computations and manipulating
computational objects within a host environment." ECMA-
262

 It is general purpose programming language.

 It is event-driven.

Javascript Engines

 Brendan Eich first engine SpiderMonkey

 Google Chrome  V8

 Safari  Nitro JavaScript engine

 Opera  Carakan

 IE 9+  Chakra

 Adobe Labs for ActionScript  Tamarin

Uses of Client-Side
Javascript
 Form Validation

 Dynamic, and Highly Responsive content.

 Personalized Interface

Where is JavaScript
added?
 In HTML file
 Between <script> tags
 Can be added to <head> section
 Mostly used to define functions
 Can be added inside <body> section

 In External file
 File will have only JavaScript Code, with extension .js
 In HTML file refer to this file using src attribute of
<script> tag

Where is JavaScript
added?
Inside HTML file In external .js file

<!DOCTYPE html> <!DOCTYPE html>
<html> <html>
<head>
<head>
<script type="text/javascript">
JavaScript goes here... <script type="text/javascript"
</script> src="file.js">
</head> </script>
<body> </head>
Mark-up goes here... <body>
<script type="text/javascript">
JavaScript goes here...
Mark-up goes here...
</script> </body>
</body> </html>
</html>

JavaScript Syntax

 Statements

 Variables

 Dialogues and Alerts

 Data Types

 Operators

 Control Statements

Statements

 JS is case-sensitive.

 Statements are places in separate lines or
separated by semi-colons on the same line.

 Comments are C/C++ like
 Single line //
 Multiple line /*………..*/

Variables

 Variable names follow C/C++ guidelines

 Variables are declared by „var‟ keyword

 A variable can be used direclty without declaring but
it is not good practice.

Try variables and dialogues
Use Developer tools

Dialogues and Alerts

 There are 3 types of dialogues
 alert()
 Show a message box with one button, has no return.
 confirm()
 Show a message box with 2 buttons (OK and Cancel).
 Returns true  OK pressed.
 Returns false Cancel pressed.
 prompt()
 Show a message box with 2 buttons (OK and Cancel) and
a textbox
 Returns the text in textbox OK pressed
 Returns null  Cancel pressed

Data Types
 Primitive Types:
 Number: float or int
 String: any charaters enclosed in “…” or „….‟
 Boolean: true/false
 Undefined
 Null

 Object:
 any value not a primitive is an object.

 JavaScript is un-typed language, thus a variable can
change it‟s type multiple times.

Useful built-in functions

 isNaN(input ) true/false
 isFinite()  true if finite number, false if not a number or
Infinity
 parseInt( input, radix=10)  NaN if failed, or number if
successful
 parseFloat(input) a floating point number or NaN
 eval(input)  tries to evaluate the input string as a
javascipt code.

Operators

 Arithmetic Operators

 Logical Operators

 Bitwise Operators (self-study)

 Comparison Operators

Arithmetic Operator

Operator Operation
+ Addition or concatenation of strings
- Subtraction
* Multiplication
/ Division
% Modulo, reminder of a division
++ Increment (post or pre)
-- Decrement (post or pre)
= Assignment
+=, -=,*=,/=, %= Compound operators

Logical Operators

Operator Operation
! Logical NOT
&& Logical AND
|| Logical OR

Comparison Operators

Operator Operation
== Equality
=== Equality and type comparison
!= Not Equal
!== Not equal with type comparison
>, >= greater than and greater than or
equal
<, <= Less than and less than or equal

Operator Precedence

 From lowest to highest
1. Assignment operators (=, +=, -=, *=, /=, %=)
2. Conditional (?:)
3. Logical or (||)
4. Logical and (&&)
5. Equality (==, !=)
6. Relational (<, <=, >=, >)
7. Addition/Subtraction (+, -)
8. Multiply/divide/modulus (*, /, %)
9. Parentheses(())

Try operators and built –in
functions on JS console
Use Developer tools

Control Statements
1. Conditional Statements 2. Loop Statements
a) if….else a) for
if (some condition is true)
for ( var i=0 ;i<10;i++)
{
{
do something;
document.write(“this is number” + i)
}
}
else
{ b) while
do something else;
} while (condition)
{
b) switch / case statements
}
switch (expression)
{ c) do…while
case label1:
statements do
[break] {
default : statements
} }while(condition)

Built-in Objects

 String

 Date

 Math

 Array

String Object

 Properties:
Property Name Description
length The number of characters in the string.

String Object (Cont‟d)

 Methods : Method Name Description
charAt(n ) Return the character at a given position

indexOf( substr,[start]) Searches for first occurrence for a
substring.
lastIndexOf( substr,[start]) Searches for last occurrence for a
substring.
toString( ) Returns the primitive string value.

toUpperCase( ) Returns with all characters converted to
uppercase.
substr(start, length) Extracts a substring of a string.

substring(from, to) Extracts a substring of a string.

slice(start , end) Extracts a substring of a string. What‟s
the difference then ??
split(delimiter, limit) Return array of strings, from splitting
string into substrings at the
boundaries specified by delimiter.

Date Object

 Object to manipulate date and time based on the
local machine time.

 Examples:
 var d=new Date() //returns date of local machine now
 var d = new Date(2008, 1, 1); //1/2/2008
 d.setFullYear(d.getFullYear( ) + 1);
//return 1/2/2009
 var weekday = d.getDay( ); //0  Sunday

Math Object

 Math is a built-in global object, which provides a
number of methods and properties that are useful for
mathematical operations, but can‟t be instantiated.

 Constant Properties:

Constants value
Math.PI 3.141592653589793
Math.E 2.718281828459045
Math.LN2 0.6931471805599453

Math Objects

 Methods
Methods
Math.abs() Returns the absolute unsigned value
Math.ceil() Return rounded number up to nearest interger
Math.cos() Returns cosine of number
Math.floor() Returns number down to nearest integer
Math.pow() Returns the number raised to a power
Math.random() Returns a number between 0 and 1.0
Math.sqrt() Returns square root of number
Math.round() Returns number rounded to closest integer

Arrays
 A datatype(object) that contains a number of other
datatypes (primitive or objects).
 An array is a data store, contains indexed elements
(index start @ 0)
 Declaring an array
 var myarr=[]; //declaring an array literal
 var myarr=[1 , 2 , ‘three’,’four’,false];
 var myarr= new Array() //using array constructor.
 Var myarr=new Array(2) //an array with 2 undefined
elements
 var myarr=new Array(1,2,’r’,true); //an array with 4
elements

Arrays (Cont‟d)
 Retrieving an element
 use the index in square brackets
 myarr[0]
 Deleting an element
 Delete myarr[2]

Array Properties

Property Description
Length Return number of elements of array

Array Methods

Method Description
concat() Concatenates elements from one array to another array.
join() Joins the elements of an array by a separator to form a
string.
pop() Removes and returns the last element of an array.
push() Adds elements to the end of an array.
reverse() Reverses the order of the elements in an array.
shift() Removes and returns the first element of an array.
slice() Creates a new array from elements of an existing array.
sort() Sorts an array alphabetically or numerically.
splice() Removes and/or replaces elements of an array.
toString() Returns a string representation of the array.
unshift() Adds elements to the beginning of an array.

Associative Arrays
(HASH)
 Arrays with index of elements a string instead of number.

 All objects are Associative arrays

 Example:
 var ar=[]; //create an array instance
 ar[„name‟]=„John Smith‟;
 ar[„age‟]=22;
 var x=ar[„name‟] or x=ar.name;

For/in loop

 Special type of for loop
 To loop over elements of an array, or properties of an
object/associative array.
 Example:
var a = ['a', 'b', 'c', 'x', 'y', 'z'];
var result = 'n';
for (var i in a)
{
result += 'index: ' + i + ', value: '
+ a[i] + 'n’;
}
alert(result);

Functions

 Functions are objects, can be returned from another functions.

 Functions are first-class citizens.

 Functions used for code reuse, information hiding, and
composition.

 Example:
function square(x)
{
return (x*x)
}

 To call it:
var x=square(4)  x=16

Functions (Cont‟d)
 Anonymous functions is a function without name

 Example:
var f=function(a,b){return a+b}

 To call it,
var x=f(1,2)  x=3;

 Self-invoked function:
 are anonymous functions invoked just after it declaration.
 To self-invoke an anonymous function add () to the end of its
definition

 Example:
var x=(function(a,b){return a+b})(1,2)  x=3

Functions (Cont‟d)

 Callback functions:
 Functions sent to other functions.
 Example:
function invoke_and_add(a, b)
{
return a() + b();
}
function one() {return 1;}
function two() {return 2;}
invoke_and_add(one, two);
invoke_and_add(function(){return 1;}, function(){return 2;})

Functions and Variable
Scope
 There is No Block Scope, all variables declared in a
function, no matter where, are defined throughout
the function.

 Variables defined in function using „var‟ (where-
ever) are local variables, if „var‟ is omitted they
become global variables.

What is the output of the
execution?
function f1(x,y)
{
if(x>3)
{
var z=3;
}
else
{
var zz=3;
}
alert(z+" - "+zz)
zzz=300;
}
f1(1,3);
alert(zzz);

What is the output of the
execution now?
function f1(x,y)
{
if(x>3)
{
var z=3;
}
else
{
var zz=3;
}
alert(z+" - "+zz)
zzz=300;
}
//f1(1,3);
alert(zzz);

What is the output ?

var scope = "global";
function f( )
{
alert(scope);
var scope = "local";
alert(scope);
}
f( );

References
 http://www.ecma-international.org/publications/files/ECMA-
ST/Ecma-262.pdf
 https://developer.mozilla.org/en-US/docs/JavaScript
 http://www.w3.org/TR/DOM-Level-3-Events/#event-flow
 http://w3techs.com/technologies/overview/javascript_library/all
 For Testing JS Compatibility:
 http://www.robertnyman.com/javascript/index.html

 Brendan Eich Blog: https://brendaneich.com/
 Useful resources:
 http://yuiblog.com/crockford/

Introduction to Client-Side Javascript

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